WITH OR WITHOUT A NURSE CROP?
The practice of sowing a nurse crop with alfalfa was inaugurated when the nature of the plant was not as well understood as now. It was also somewhat on the theory too that “a half-loaf is better than no bread.” It began when there was a good deal of doubt about “getting a stand,” and the farmer thought no doubt that a crop of oats or barley would pay for the plowing even if the alfalfa failed. While the practice is continued by many, the prevalent later method is to provide no nurse crop. Few who have abandoned the nurse crop have returned to it. The alfalfa plant does not need protection from the sun, nor is it bettered by dividing any of the soil moisture or fertility with those of another crop. On the other hand, if alfalfa is sowed in the spring, it is important that it obtain an early start in order that its roots can quickly work their way down into the moisture of the subsoil, against the dry days of July and August. When a nurse crop of any vigor is removed the alfalfa plants are likely to be found weak, spindling and with little root growth; the nurse crop also has taken up some of the soil nitrogen needed by the young alfalfa; or if the nurse crop is heavy and has lodged, there will be left bare spots, where the alfalfa has been smothered out.
Cutting the nurse crop is likely to be attended with no little damage to the tender alfalfa plants by trampling their crowns into the ground, or by breaking them off. Practically all the experiment stations favor sowing alone. With few exceptions the second and third years have brought heavier yields where no nurse crop was used. The theory that the nurse crop will prevent the weeds choking the alfalfa is apparently, as a rule, not well founded. In the first place alfalfa should not be sown on foul land, and in the second place proper disking and harrowing, at near intervals for four or six weeks before sowing, will disturb or kill far more weeds than can any nurse crop. Besides, the oats or barley sown as a nurse will when cut leave weeds in good growth, or dormant and ready to spring up as fast or faster than the alfalfa. No nurse crop is ever used with fall sowing. When ground has been thoroughly prepared for the preceding crop, and then properly cared for, and made ready for the alfalfa by the preliminary weed destruction, it will be found advisable to sow alfalfa alone, even in the spring.
INOCULATING THE SOIL
It has been found where alfalfa shows thrifty vigor, is making a good stand, and is at least two years old, that on the roots are little nodules or wart-like protuberances. On fields where the alfalfa is unthrifty or failing to make a good stand, examination will probably fail to discover any of these nodules. Scientists tell us that these nodules are the homes of bacteria, microscopic vegetable organisms obtaining their sustenance from the nitrogen of the air and the starch of the plant; that they collect much more nitrogen than they need, the over-supply being taken up by the alfalfa, which, after these nodules are formed and occupied, takes no more nitrogen from the soil, but annually stores about its roots more from the air, thus adding to the nitrogen supply in the soil instead of taking from it as do all other farm crops except the legumes. Each legume—clover, alfalfa, cowpeas, etc.—has a distinct species of bacteria, or at least bacteria with a distinct development, excepting, as has been found, that Sweet clover (Melilotus alba) and Bur clover (Medicago denticulata) develop the same species as does alfalfa.
BUYING INFECTED SOIL
Several methods of preparing land for alfalfa by introducing its peculiar bacteria have been suggested, and practiced to some extent. Many farmers and experimenters have used with success infected soil upon their lands; soil from established alfalfa fields, or that from along the roads or creeks where the Sweet clover or Bur clover has been growing. This soil is spread upon the field or sown with alfalfa just before the seeding. If the drill is to be used the inoculated soil is spread on and harrowed in. If the seed is to be broadcasted, the infected soil may be harrowed in with the seed. It is better, however, to harrow this infected soil in thoroughly before seeding. Experiment stations recommend an application of two hundred pounds of such soil to every acre, but good results have been secured from half that quantity. This will depend very much upon the nature of the soil, and the subsoil especially. Many fields seem to have these bacteria waiting for the coming of alfalfa. Land that has been well manured and contains abundant humus, and land that is light and friable will usually respond to the bacterial life attached to the alfalfa seed. Most farmers who have established fields will sell soil to their neighbors, which should be from the top six or eight inches, and include roots, stubble and earth. Both Sweet clover and Bur clover are found in almost every neighborhood in the northern states, while the latter is very general in the South.
Some alfalfa raisers make a business of selling and shipping inoculated soil. Probably any experiment station will ship small quantities to farmers within its state, at about the cost of digging, sacking and delivering at the railroad station. Therefore, if a farmer desires to use it, little labor or expense is attached to doing so. There is reason, however, to doubt the need of this method in any of the western or central western states where the suggestions mentioned in the first part of the chapter are closely followed. No doubt there are advantages in using it in most states east of the Mississippi river, in order to hasten the development of the bacteria and to make a good stand more certain. Preparation one or two years in advance as already described, by a light sowing of alfalfa seed for introducing its peculiar bacteria, is less expensive, and requires less labor and carries no risk of introducing the seeds of other clovers or weeds. Most farms have enough weed seeds already.
DANGERS OF INOCULATION BY SOIL TRANSFER
Touching upon the dangers possibly resulting from inoculation by soil transfer a bulletin from the United States Department of Agriculture has this to suggest: